In electrical manufacturing industries generally, and specifically in the appliance manufacturing industries, the National Electric Code permits circuits used to operate appliances to be rated for power consumption (or maximum current consumption) that is significantly less than the sum total of all the power loads that may be energized or actuated in an individual appliance. The reasoning behind this standard is that in normal operation not all of the available appliance electrical components can or will be operated simultaneously. Typically, even during a heavy power usage condition where a plurality of loads are simultaneously drawing current, the circuit breaker current trip curve permits the electrical loads connected thereto to exceed the breaker rating for very short time periods. Accordingly, many new appliances are presently designed such that their electrical components, if energized simultaneously, will far exceed the circuit breaker ratings for the circuits supplying them with electrical power.
The overall design trend as appliances become more sophisticated is for most devices to be designed with more electrical components, thus increasing the number of electrical loads that may be drawing current at any time in any one appliance. This tendency makes it more common for appliances to trip circuit breakers during what many would consider “normal” operation of a specific appliance. In order to avoid and minimize circuit breaker trips many manufacturers have designed power sharing or power management systems into their appliances.
Prior art appliance power management systems vary widely in design but often come in two categories. Many hardwired power management systems utilize current transformers or equivalent sensors to determine current demand, and then utilize hard-wired automatic switching circuits employing relays to reduce or cut-off power to some electrical components that are considered non-critical. Other power management systems utilize various processors and feedback control loops to monitor and adjust power usage based on direct feedback and prioritized load usage. Additionally some systems combine these two general techniques to achieve efficient power management.
There are various disadvantages to each of these approaches to power management. Hardwired systems typically employ a great deal of complex circuitry and usually require a good deal of additional hardware to implement. These systems can be quite expensive to design and build, and once implemented they do not have the ability to intelligently adjust power consumption based on changing variables. Processor and feedback control power management systems offer a greater degree of control and flexibility but also require a large number of additional sensors and hardware that necessarily add cost and complexity to the appliance design.
From the foregoing it can readily be seen that there is a need in the art for a power management system that can be employed with individual appliances to control overall power usage in the appliance without adding significantly to the cost and complexity of the devices.